Electric contact

ABSTRACT

An electrical contact, especially an electrical contact of a plug connector, includes a metallic substrate on which a contact layer is applied in the form of a gradient layer. The gradient layer is formed by at least two elements of which one is silver and forms a matrix for the second element or forms an alloy therewith, or of which one is tin and the other is phosphorus or of which one is indium and the other is tin.

FIELD OF THE INVENTION

The present invention is based on an electrical contact, in particularan electrical contact of a plug connector.

BACKGROUND INFORMATION

An electrical contact is described in U.S. Pat. No. 5,892,424 andrepresents an encapsulated point of contact of an electrical connection.The known electrical contact is made up of a substrate on which acontact layer is deposited to reinforce the wear resistance of theelectrical contact. This contact layer has a matrix formed from a firstelement, which is doped by a second element. The matrix can be made upof an element selected from the group that includes Mo, Zr, Nb, Hf, Taand W. The additional element may be an element selected from a groupthat includes Zn, Cd, Hg, Al, Ga, In, Tl, Ge, Sn, Pb, As, Sb and Bi. Theadditional element stabilizes the contact resistance of the electricalcontact during an electrical switching operation. Furthermore, theadditional element leads to an improvement in the wear resistance andthe oxidation resistance of the electrical contact. The proportion ofadditional elements in the contact layer may amount to between 0.5 atom% and 50 atom %.

The contact layer in the known electrical contact is applied accordingto a sputtering method, an ion-supported vapor-deposition method, anion-plating method or a plasma CVD method. However, due to a requiredultra-high vacuum, these methods are involved and not suited for theproduction of high quantities.

Furthermore, the metals from which the contact layer of the knownelectrical contact is made, are expensive and therefore also notsuitable for contacts that are required in large numbers. This appliesespecially to electrical contacts in motor vehicles, which are requiredin quantities of 1000 to 3000 pieces per motor vehicle.

In practice, electrical contacts in the automotive sector often have acontact layer made of tin. This layer may be a hot-dipped or agalvanically deposited layer having a thickness of a few micrometers.Tin is characterized by its ductility as well as its excellentelectrical conductivity. When using a tin contact layer, diffusioncauses an intermediate layer to be formed at the boundary surface to thesubstrate, which normally is made of an alloy on copper basis such asCuSn4 bronze, CuNiSi or the like, the intermediate layer consisting ofintermetallic compounds such as CuSn3, Cu5Sn6. The intermediate layer isharder than the contact layer and may grow as a function of temperature.

However, tin alloys or tin-alloy layers have the disadvantage that theytend to wear off due to their low hardness and the resulting low wearresistance during frequent plug-ins or due to vehicle- or engine-relatedvibrations, thereby causing increased oxidation—the so-called chafingcorrosion. The erosion and/or chafing corrosion in turn may lead tomalfunction of an electrical component of a motor vehicle assigned tothe contact in question, for instance a sensor, a control unit or thelike.

Another disadvantage of such tin layers is that, because of the highadhesion tendency and the plastic deformation of these contact layers,the plug forces are too high for many application cases.

Also known from practice is a contact layer of an electrical contactmade on the basis of tin—also referred to as thermo-tin—, which iscompletely made of intermetallic phases and produced by heat treatment.Abrasion tests have shown such contact layers to be of limited use too.

In addition, AuCo alloys with a tin undercoat, silver layers with acopper undercoat or a tin undercoat or also gold layers are currentlyoften used as contact layer in electrical contacts.

Surface or contact layers on the basis of silver, in particular, but tinas well, exhibit a cold welding tendency due to adhesion and, whencombined with each other, are characterized by high frictioncoefficients.

Even with silver or gold layers currently used in electrical contacts,oxidative wear processes of the substrate or an intermediate layer—oftenmade of copper or nickel and used as an adhesion layer—may occur oncethe layer has eroded or chipping has occurred in the layer.

SUMMARY OF THE INVENTION

The electrical contact according to the present invention, which has ametallic substrate on which a contact layer in the form of a gradientlayer is applied that is formed by at least two elements of which one issilver and forms a matrix for the second element or forms an alloytherewith, or of which one is tin and the other is phosphorus or ofwhich one is indium and the other is tin, has the advantage that, as aresult of the components used for the contact layer, their availabilityand their relatively low procurement costs, it constitutes a contactlayer which is suitable also for electrical contacts required in highquantities.

A gradient layer within the meaning of the present invention is to beunderstood as a contact layer in which the proportion of the twoelements changes in the direction of the normal of the substrate plane.For instance, the tin proportion in a silver matrix or silver/tin alloymay decrease in the direction facing away from the substrate. The changein the element proportions of the contact layer may be linear, in whichcase a linear concentration gradient is present. As an alternative,however, it may also be a concentration gradient that varies accordingto a step function. The proportion of the one element in the contactlayer basically may run the range between 0% and 100% in the gradientdirection.

The substrate is, for instance, a substrate conventionally used inplug-in connections in the automotive sector, for example an alloy oncopper basis such as CuSn4 bronze, CuNiSi or the like. As analternative, a substrate made from an alloy on tin basis may be used aswell.

If one of the two elements in the electrical contact according to thepresent invention is silver, which forms a matrix for the second elementor forms an alloy together with the second element, the second elementor the additional element may be tin, gold or indium as well.

The gradient layer preferably has a thickness of approximately 1 μm to 3μm, but may also be implemented at greater thicknesses.

To improve the contacting between the electrical contact and its matingcontact, the gradient layer may have a noble-metal cover layer, at leastregionally. The noble-metal cover layer preferably is between 0.1 μm and0.3 μm thick and thus constitutes a so-called “flash” layer. Au, Ru, Ptand/or Pd are especially suitable as noble metals for the flash layer.

The contact layer is preferably produced according to a galvanic methodor also according to a PVD (physical vapor deposition) method.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a section through an electrical contact according tothe present invention.

DETAILED DESCRIPTION

The FIGURE shows an electrical contact 1, which represents a contact ofa plug connector as it is used in an automobile.

Electrical contact 1 includes a substrate 2, which is made of an alloyon copper basis such as CuSn4, CuNi2Si or the like. Substrate 2 has athickness that is between 0.1 mm and 0.5 mm.

A contact layer 3, which is applied according to a galvanic method, isarranged on substrate 2 of electrical contact 1. Contact layer 3constitutes a silver/tin substance system, the silver and tin forming analloy with one another. The tin concentration in contact layer 3decreases in an essentially linear fashion in the direction facing awayfrom substrate 2, for instance from approximately 100% to approximately20%. Contact layer 3 thus forms a gradient layer.

The thickness of contact layer 3 is in a range between approximately 1μm and 3 μm.

Arranged on the upper surface of contact layer 3 is a so-called goldflashing or “flash” gilding having a thickness of approximately 0.2 μm,which is configured as cover layer 4.

In an alternative specific embodiment of an electrical contact, thegradient points in the opposite direction, so that the tin concentrationin the contact layer increases in the substrate direction and thehighest silver concentration therefore is present on the surface of thecontact layer or gradient layer.

1. An electrical contact comprising: a metallic substrate; and, acontact layer in the form of a gradient layer applied on the metallicsubstrate, the gradient layer being composed of at least two elements,the at least two elements including a first element and a secondelement, wherein one of: (a) the first element is silver and forms analloy with the second element, the second element including one ofindium and tin, (b) the first element is tin and the second element isphosphorus, and (c) the first element is indium and the second elementis tin; wherein a proportion of the first element and the second elementin the gradient layer changes substantially linearly in a directionnormal to a plane of the substrate.
 2. The electrical contact accordingto claim 1, wherein the gradient layer has a thickness of between 1 μmand 3 μm.
 3. The electrical contact according to claim 1, wherein thegradient layer has a noble-metal cover layer at least regionally.
 4. Theelectrical contact according to claim 3, wherein the noble-metal coverlayer has a thickness of between about 0.1 μm and 3 μm.
 5. Theelectrical contact according to claim 3, wherein the noble-metal coverlayer is composed of at least one of Au, Ru, Pt and Pd.
 6. Theelectrical contact according to claim 1, wherein the gradient layer isapplied on the substrate according to one of a galvanic method and a PVDmethod.